Slicing and dicing with Occam's razor, testing the board on 120 volt is pretty easy- the only part of the board that can cause that malfunction is really the relay contacts being bad, and cutting the power going to the element. They also have to be *not too bad*, or the board would detect the error, as it monitors both voltage and current to the element.
So- to test the relay, turn it on Elec., make sure it is calling for cooling, measure the voltage at the board input and output. If they are the same, the board is good. If they are different, the board is bad (at least the relay is bad).
While there could be spooky software glitches, the majority of them would have external causes- rf interference and/or dirty DC power.
